The disclosures herein relate generally to heat dissipation and more specifically to heat dissipation within a portable computer.
A portable computer is a self-contained personal computer which can be easily moved to and operated at various locations. Portable computers are often referred to as laptop or notebook computers. To be portable, these computers must be small, compact, and lightweight. The conventional portable computer includes a base portion and a lid portion that pivotally opens from the base portion when the portable computer is in use. The lid portion contains a flat panel display such as a liquid crystal display (LCD) or other suitable display.
Portable computers are being required to accommodate increasingly higher thermal loads. Central Processing Unit (CPU) power requirements are increasing along with other higher-power motherboard components. In order to cool the computer properly, larger cooling solutions are being implemented, which include heat spreaders, heat sinks, fans, and heat pipes.
One known type of heat spreader used for distributing heat away from a processor in a portable computer is a piece of metal thermally coupled to the processor. Such a heat spreader is typically made of relatively pure aluminum. Aluminum exhibits good thermal conductivity and has reduced weight over other types of metal. However, aluminum is subject to oxidation, whereby aluminum oxide coatings typically form on the outside surfaces of exposed aluminum. In the case of an aluminum heat spreader, aluminum oxide reduces the ability of the aluminum heat spreader to provide for a low impedance thermal connection.
In addition to heat spreaders, the combination of fans and heat sinks have been used to provide cost effective mechanisms for thermally managing the cooling requirements of many types of computer systems. However, fans require power and heat sinks require space. While power and space are generally in abundant supply in rack and desktop-type computers, portable computers have only a limited supply of both power and space. An operable fan may unduly draw upon the batteries of a portable computer, thus making the fan and heat sink cooling solution unattractive for long periods of battery-powered portable computer operation.
Heat pipes offer another option for a cooling solution. Heat pipes are self contained, phase transformation, heat carrying devices, i.e. each is a superconductor of heat. A typical heat pipe may comprise a closed copper tube having a partial vacuum internally. Pre-existing liquid, such as water, CCFC, or other suitable liquid, in a hot portion of the tube boils at a lower than usual temperature in the partial vacuum. The boiling liquid forms steam, which seeks a cooler spot. The steam moves to carry heat to the cooler spot where the steam condenses to cooler liquid. The cooler liquid then returns to the hot spot. The cycle is ongoing, which provides a self-contained circulating cooling system.
The following U.S. patent addresses the issue of heat dissipation within a computer. U.S. Pat. No. 5,598,320 discloses a rotatable and slidable heat pipe apparatus for transferring heat away from a microprocessor chip more rapidly than by heat sink surface area dissipation to the surrounding air alone. The apparatus includes a heat sink with an integral cylindrical passageway adapted to receive a first end of a heat pipe shaped like a crankshaft and a heat spreader formed from a metal plate with a first end rolled up to define a cylindrical opening adapted to receive a second end of the heat pipe. The heat spreader is attached to an underside of a keyboard. Since the heat pipe is able to rotate within the cylindrical passageway and the cylindrical opening, the keyboard can be raised to an open position and lowered to a closed position quickly and simply without the risk of breaking or bending the heat pipe, and manufacturing position tolerances between the heat pipe apparatus components are increased resulting in a simplified manufacturing process. The heat pipe can also be slid in and out of the cylindrical passageway or the cylindrical opening, thereby enabling computer manufacturers to incorporate the heat pipe into portable battery powered notebook-type computer systems designed to allow a user to remove, replace, or swap internal components by simply flipping open or removing the keyboard, and further enabling a user to perform maintenance work or repairs on the computer system without concern for damage to the heat pipe.
Co-pending U.S. patent application Ser. No. 09/170,510 is another example that addresses the issue of heat dissipation within a computer system. In the embodiment of FIG. 1, a first end of a heat pipe 2 is connected to a heat sink 4 by a rotatable thermal connection 6. Heat sink 4 is mounted on and fastened to a bottom member 16. Rotatable thermal connection 6 enables heat pipe 2 to retract from a first position to a second position, indicated in FIG. 1, to allow a CPU 8 to be installed directly on top of a motherboard 10. Once CPU 8 is installed, heat pipe 2 is rotated back to its first position, represented in FIG. 2, in order for a thermal block 12, which is connected to a second end of heat pipe 2, to be thermally coupled to CPU 8. A set of mounting screws 14, or other suitable fasteners, are then used to secure thermal block 12 to CPU 8.
In a build-to-order computer system manufacturing process, custom configured computer systems are assembled with hardware and software based upon a customer order. With respect to portable computers, in order to fulfill build-to-order manufacturing requirements, the CPU is preferably installed at final assembly. For the vast majority of portable computer layouts, the CPU is directly on top of the motherboard and the CPU cooling solution installed on top of the CPU. While cooling solutions can be installed after installation of the CPU, some layouts cause the cooling solution to be trapped under a palmrest and LCD. Therefore, in order to install the CPU during the build-to-order manufacturing process, either the palmrest and/or LCD assembly must be installed after the cooling solution is installed. Unfortunately, this method is undesirable since it requires additional disassembly/assembly procedures in the build-to-order manufacturing process. Further, a greater inventory of component parts is required to be maintained.
Accordingly, an improved cooling solution that can be installed in a portable computer prior to the installation of the CPU during the manufacturing process is desired.